Endeavour of a worker to come in sober (7)
I believe the answer is:
attempt
'endeavour' is the definition.
(synonyms)
'a worker to come in sober' is the wordplay.
'worker' becomes 'temp' (temp is a kind of worker).
'to come in' is an insertion indicator.
'sober' becomes 'tt' (I've seen this in other clues).
'temp' put within 'tt' is 'ttempt'.
'a'+'ttempt'='ATTEMPT'
'of' is the link.
(Other definitions for attempt that I've seen before include "Try to climb (a peak)" , "Try, hazard" , "Effort; go" , "Stab" , "Embark on, try" .)